Cyclic gear mechanism



'0. H. PETERSEN CYCLIC GEAR MECHANISM Filed sept. 9, 1949 Inventor:

His Attorneg.

Otto H. Petersen,

b5 mv 9m Oct. 2, 1951 Fg I.

Patented Oct. 2, 1951 UNITED STATES OFFICE CYGLIC GEAR MECHANISM Otto H.` Petersen, Fayetteville, N. Y.,.assgnor .to

General ElectricCompany, `a, corporation of` New York Application September 9, 1949, Serial No. 114,711

(Cl. i4-7.99)

2 Claims. I

This invention relates generally to cyclic gear mechanisms and more particularly to la specific form of such a mechanism utilizing beveled gears ina differential arrangement.

The use of cyclic gear trains for effecting speed reductions is well known. For instance, suchcyclicreductiontrains `are encountered in screw machines, in lathe controls, in dial drive mecha.. nisms,A and in automobile transmission systems.`

Inw applications where freedomfrom backlash in the gears is not particularly important, there is no particular difliculty in cutting gears in a -manneri-to insure complete freedom fromf binding.-

Howeverywhere the backlash: must be kept to a minimum, special `measures must be taken to prevent binding andto insure smooth: operation. It is an object of my .invention to provide a new andimproved cyclic gear mechanism having practically complete freedom-'from backlash.

Another object of my invention is to. provide a reduction drive mechanism utilizing bevel gears ima differential arrangement that permits sub-i stan-tially complete freedom from backlash without :any I. tendency towards binding;

-Afurther object of myinventionis to provide anew landV improved system for mating bevel gears-.in `a differential arrangement whichrehaves-the gears of the .functionfof -lwithstanding unavoidable thrusts. and thereby reduces. any tendency on the part ofthe gears to` bind and wear4 unnecessarily.

For further objects and advantages and for -a better. understanding of the-invention,- attention isnowdirected to the following description.- The features-of my invention believed to be novelV wi-llbe more particularly pointed out in the appended claims.

Myinvention is particularly concerned withl a reduction gear mechanism lfor controlling deli-- cate-apparatus. However, -it ism-no wayrestricted -to such an` application. and the featureslarly toFig. 2, there is shown a shaft Ill .project-,-

ing-through a mounting plate -:I I. The function oiithe mechanism, which `will, now be described,- isfto ,permit a reduced drive of the shaft lli by rotation of a knob I2, which is pivotally mounted on a pin I3, secured-to acasingjfby means of a set screw I5.

The drive from the casingltorthe shaftl is" provided through the medium of a pair of beveled sun-gears Itand I'I facing each other,.-

and a pair of beveled pinions I8 and I9 which operate gas planet gears.

two screws 201 and 2I are visible in Fig. l. gear Il is likewise secured to plate II by means of suitable screws, of which one screw 22 is visible in Fig. 2. Beveled pinions I8 and |91 are mounted onspider` shafts 23 and 24 which project--` radially from a circular hub 25, the whole constitutingwhat is commonly referred to as-a spider.; The spider is fastened to the shaft I0 by meansl of a pair of set screws 26. The casing I4 is rotateably mounted on the hub 25 and is held by means of a nat-headed screw 27 which is threaded into hub 25 and abuts against a collar 28, press-fitted' into the casing I4.

The construction of the mechanism, to theextent that it has been described above, is well,-

In operation, the spider is maintained in axial position by its fastening tothe shaft It, and the "casing I4 is rotatably--M Sun gears I6 and I'Iv are provided with identical tooth configurationsand mesh with tbe planet gears carried on the4 known in the art.

mounted on the spider.

spider. When the casing I4 is rotated, sun gear It moves with it and engages planet gears I 8-` and I9,` causing them to spin on the radial spider shafts` 23 and 24 at a rate determined by theV relative rotation `of member 25 with respect to the Casing I4; Howevensince the planetgears also engage the stationary suny gear I1,mern ber 25, has a relative motion in a` positive sense with respect to gear Il, equal toits relative motion ,Y

in anegative, sense with, respect to gear` I6. As

a result, the hub 25` rotatesat half `the absolute. speed ofcasing I4, and thereby provides a reduc-` tion .in the ratio of one to .two in the driveV of shaft II).

The structure of kthedrive mechanism as thusY far described would normally require any thrust transmitted from `casing I4. Ato shaft I0 to, be

taken up by the tooth surfaces of sun gears I6` and I 'I against the tooth surfaces of planet gears,

mand i9. Under these conditions, since it is necessary to cut the toothconguration' to very close `tolerances in order to .eliminate backlash,

binding is apt to occur. The features` of my in-` vention which will now be described permit cuttingthe teeth to close tolerances and also permit the adjustment of the planet gears to provide-- a practically complete elimination of backlash,-

without incurring any risk of binding.

In accordance with my invention, instead of* requiringthe planet gears to take up the axialthrust of the casing is, `a form of roller`bearing is provided for the purpose. Referring to Fig. 2, a disk or roller 2t is rotatably mountedl ona collar provided by` an outward projection of the hub of planet gear I8. A similar rollerv 3B; is mounted `on the hub of planet gear I 9. These rollers bear against the inner face-of casing-I4 on--onegsidej, and against a ring3|` on;- Ring 3l -islaid-flatl against--z the other i side-.-

Sun gear I6 is secured to casing IA-byfmeans of four screws, of which Sun mounting plate II and is concentric with ring gear I1. The inner face of casing I4 and the opposing face of ring 3I serve as races on which rollers 29 and 30 run. .There is thus provided a form of roller bearing which takes up the axial thrust of casing I4 against shaft I0. and which also serves to maintain the planet gears I8 and I9 accurately positioned with respect to the sun gears I6 and I1.

'I'he tWo rollers 29 and 30 are suiicient for the purpose for which they have been provided, but. as a further refinement I have provided a second pair of rollers 32 and 33. These are mounted on a second pair of spider shafts 34 and 35 which extend axially from hub 25 and at right angles tothe first set of spider shafts 23 and 24. Rollers 32 and 33 are mounted on collars 35 and 31, which locate them on their respective spider shafts in the same manner as the hubs of planet gears I8 and I9 locate rollers 29 and 30. In practice, the planet gears and the ring gears are preferably made of brass and the spider shafts and the rollers are preferably made of steel.

The rollers thus provide a practically frictionless means of axially locating the spider with respect to casing I4 and plate II, and thereby control the meshing of the planet gears with the sun gears. When casing I4 is rotated, the rollers-Spinat substantially the same speed as the planet gears. However, the rollers take up the axial thrusts, and the function of the planet gearsis then limited ,to establishing the speed ratio. Since the planet gears are not required to take up any axial thrusts, they may now be machined to -much closer tolerances, in order to eliminate backlash, and binding does not occur.

In accordance with a Vfurther feature of my invention, spider shafts 23 and 24 can be adjusted radially with respect to hub member 25, and likewise spider shafts 34 and 35. The spider shafts are locked in place by suitable set screws, such as set screw 38 in Fig. 2, and 39 in Fig. 3. In adjusting the mechanism, the spider shafts 23 and 24 are pushed radially inward towards the axis of member 25, until a point is reached Where the planet gears I8 and I9 roll freely and without backlash on sun gears I6 and I1. This feature permits a very ne adjustment of the mechanism and eliminates the necessity of relying entirely on'accuracy in machining the gears for the prevention of backlash.

Although a specific embodiment has been shown and described, it will, of course, be understood that various modifications may be made without departing from the invention. For example, while the rollers 29 and 39 are preferably rotatable with respect to planet gears I8 and I9, they may alternatively be integral therewith. In such case, the bearing surface of the roller portion should lie approximately on the pitch line of the associated gear portion to avoid' undue roller slippage. It is also apparent that in some cases it may be desirable to have planet gears on all four spider shafts. The appended claims are therefore intended to cover any such modications falling within the true spirit and scope of the' invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A cyclic gear mechanism comprising a pair of spaced sun bevel gears mounted in parallel planes in mutually facing relationship on an axis-a hub member, a pair of stub shafts each aiixed to said hub member at one end and extending therefrom in diametrically-opposite directions, a pair of planet bevel gears respectively mounted on said stub shafts, said hub member being interposed between said sun gears and, in combination with said stub shafts, constituting a spider rotatable on said axis, said planet gears each meshing with both said sun gears, a pair of xed bearing races concentrically mounted with respect to said sun gears and in similar opposing relation, a pair of rollers rotatably mounted on 'said respective shafts and each bearing against both saidraces for accurately positioning said spider between said sun gears, and means for individually adjusting each of said shafts radially to provide accurate adjustment of the meshing of said gears.

2. A cyclic gear reduction mechanism comprising a mounting plate having an opening therein, a driven shaft extending through said opening in a transverse direction, a hub member secured to said shaft, a pair of diametrically opposed radial shafts affixed to said hub member, a driving casing rotatably mounted on said driven shaft, a pair of similar sun bevel gears located in parallel planes in mutually facing relationship and concentric with the axis of said driven shaft, one of said sun gears being affixed to said rotatable casing and the other being aixed to said mounting plate, a pair of similar planet beveled gears respectively journaled on said diametrcally opposed radial shafts, said hub member being interposed between said sun gears and, in combination with said radial shafts, constituting a spider rotatable on said axis, said planet gears each meshing with both said sun gears and thereby causing said driven shaft to be driven through said spider, in response to rotation of said casing, so as to rotate at half the rate of said casing, a pair of races concentrically mounted with respect to said sun gears and having opposed fiat surfaces parallel to said planes, said races also being respectively affixed to said casing and said mounting plate, a pair of rollers also rotatably mounted on said respective radial shafts, said rollers each being constructed and arranged to bear against both said races for accurately positioning said spider between said sun gears and to take up thrust transmitted through said casing to said driven shaft, and means for individually adjusting the radial spacing of each of said planet gears from said axis, thereby to provide accurate adjustment of the meshing of said planet gears with said sun gears.

OTTO H. PETERSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 741,931 Sandell Oct. 20, 1903 941,101 Ross Nov. 23, 1909 1,414,479 Mays May 2, 1922 1,484,565 Rikes Feb. 19, 1924 1,527,335 Uppercu Feb. 24, 1925 1,786,338 Donohue Dec. 23, 1930 1,970,251 Rossmann Aug. 14, 1934 1,994,719 Lichty Mar. 19, 1935 FOREIGN PATENTS Number Country Date 81,234 V Germany May 23, 1895 l 

